This invention relates generally to hand tools and related manufacturing processes. More particularly, this invention relates to an improved impact or striking tool of the so-called nonrecoil or nonrebound type, such as a hammer or mallet, having an impact head constructed in accordance with an improved and simplified manufacturing process.
Impact tools of the so-called nonrecoil or nonrebound type are generally known in the art, such as a hammer or mallet having an impact head constructed to absorb and dissipate striking forces and thereby reduce or eliminate the bounce-back or rebound effect which normally occurs after striking a surface. Such impact tools typically have a hollow core canister or head filled partially with a relatively high mass and flowable filler material such as steel shot pellets, steel pins, or the like. In many designs, the hollow canister is protectively encased in whole or in part within a molded jacket or cladding constructed from a selected tough and durable thermoplastic material such as nylon. In use, when the tool head is impacted with a target surface, the filler material shifts and slides about within the hollow canister to absorb and dissipate the impact force and thereby effectively counteract any resultant rebound force. For examples, of such nonrecoil impact tools, see U.S. Pat. Nos. 5,262,113 and 5,375,486.
In the past, efforts to utilize a lightweight hollow canister in constructing a nonrecoil impact tool have encountered manufacturing problems during the molding step for encasing the hollow canister within the durable plastic jacket. More specifically, in this molding step, the hollow canister is placed within an injection mold and the plastic jacket material is then injected into the mold under substantial heat and pressure. When a lightweight canister of thin-walled metal or molded plastic material is used, the jacket molding parameters can cause undesirable distortion and deformation of the hollow canister sufficient to interfere with the desired shifting of the filler material to dissipate impact forces during use of the tool. In the past, this canister deformation problem has been addressed by completely filling the hollow canister with the filler material, whereby the filler material provides a rigid structural backstop to preclude deformation during the jacket molding step, after which a portion of the filler material is then removed from the canister through an open drain port or gate. However, this approach requires additional manufacturing steps such as post-molding removal of the excess filler material as well as the need to close the drain port. See, for example, U.S. Pat. Nos. 5,262,113 and 5,375,486.
The present invention overcomes these problems and disadvantages by providing an improved impact tool having a hollow core canister filled partially with a flowable filler material, but wherein the hollow canister is designed to withstand heat and pressure encountered in the course of a jacket molding step without significant risk of canister deformation or collapse, and further without requiring post-molding removal of any portion of the filler material.